Circuit/System Testing

DTC P0171 or P0174 

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be less than approximately 24 percent with the engine running at operating temperature.

• If the value is more than 24 percent, inspect for the following:

• With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .
  • If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106  and DTC P0107 or P0108 .
• Vacuum hoses for splits, kinks, and improper connections
• Insufficient fuel in the tank
• A malfunctioning MAF-Refer to DTC P0068 or P0121  or DTC P0101 or P1101 .
• Low fuel pressure
• Fuel contamination
• Malfunctioning fuel injectors
• Missing, loose, or leaking exhaust components from the HO2S forward
• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
• The air induction system and the air intake ducts for leaks or for a missing air filter element
• A cracked or damaged EVAP canister
• Evaporative canister purge lines plugged or obstructed
• The crankcase ventilation system for leaks
• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit
• The HO2S sensor 1 low signal circuit for an open circuit or high resistance
• Malfunctioning engine components

DTC P0172 or P0175 

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be more than approximately -23 percent with the engine running at operating temperature.

• If the value is less than -23 percent, inspect for the following:

• With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19-42 kPa.
  • If the MAP sensor parameter is not between 19-42 kPa, refer to DTC P0106  and DTC P0107 or P0108 .
• Vacuum hoses for splits, kinks, and improper connections
• The inlet screen of the MAF sensor for blockage
• A malfunctioning MAF-Refer to DTC P0068 or P0121  or DTC P0101 or P1101 .
• The air duct for being collapsed or restricted
• The air filter for being dirty or restricted
• Objects blocking the throttle body
• Excessive fuel in the crankcase
• The evaporative emissions control system for improper operation
• Excessive fuel pressure
• Improperly functioning fuel injectors
• Fuel contamination
• The HO2S for proper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit shorted to voltage